Make sure you've thoroughly read the requirements for the position and confirm that you meet them. Refer to specific responsibilities of the position and tie them to your educational and/or professional experience. If you aren't applying to a specific internship/training opening and are proposing the program to the employer, be sure to explain that you have a strong foundation for training in this industry. They will understand that they will need to teach and train you, but they will also want to know you have sufficient preparation to be successful.